Integrated circuit chips, such as micro-processor chips, and other electronic components generate heat during operation. These components are generally mounted on printed circuit boards (PCBs). To help ensure proper operation, these components must generally be kept at an operating temperature below about 160° F. This means that cooling of some sort must ordinarily be provided for proper operation of the electronic components.
Cold plates are widely used for cooling PCBs where the coolant must be kept separated from the electronic components. A cold plate generally consists of an enhanced heat transfer surface encapsulated in a high aspect ratio rectangular duct. The enhanced heat transfer surfaces are typically some sort of fin arrangement or an open-celled, porous metal foam. Coolant flows through the cold plate from one end to the other end, wetting the enhanced heat transfer surface inside. This system cools PCBs mounted to the sides of the cold plate. Finned core stocks and metal foams are used in cold plates because they increase the thermal effectiveness by increasing the surface area available for transferring heat to the coolant. However, surface area densities for finned core stock and metal foams are generally limited to approximately 1000 ft2/ft3. This is chiefly because surface area densities significantly larger than this value result in unacceptably high pressure drop as the coolant flows through the cold plate. High pressure drop translates into a system penalty in the form of higher power required for pushing the coolant through the cold plate. Furthermore, manufacturing fin and metal foam arrangements with higher surface area densities becomes increasingly costly and complex. These limitations on surface area density ultimately limit the heat that can be absorbed for a given coolant flowrate. In the future, such a limitation will be exacerbated by the introduction of high power electronics, including high power chip designs, because conventional air cooled cold plates will not be able to meet cooling demand. These future electronics are projected to generate significantly more heat than contemporary electronics while still having an operating temperature limit of about 160° F.
When applied to conventional avionics PCB's, conventional cold plates require a large amount of coolant because they are not very efficient. This constitutes a significant penalty for an air vehicle because cooling air generated by the aircraft Environmental Control System (ECS) by cooling and conditioning air extracted from the engine(s) that would otherwise provide thrust to the air vehicle. Metal foam solutions could conceivably meet some future PCB requirements, but they need significantly larger coolant flow rates that are a great burden on the air vehicle.
Cold plates may also be used as heat exchanger cores. Conventional heat exchangers cores are typically heavy, costly brazed plate fin designs made from a high conductivity metal. Likewise, metal foam cores for heat exchanger applications are expensive to construct. Furthermore, the limited thermally efficiency of conventional designs means that a more efficient design would need significantly fewer cores to achieve a particular effectiveness level. Conversely, a more efficient design would give a higher effectiveness for the same number of cores as found in conventional designs. Fewer cores would result in a lighter, less costly heat exchanger that would take up less space on an air vehicle.
In summary, it would be desirable to reduce the amount of air required for cooling conventional avionics by increasing the heat transfer ability of a cold plate, thereby reducing the system performance penalty. It would further be desirable to address cooling of future high power electronics that are projected to generate significantly more heat than contemporary chips while still having an operating temperature limit of about 160° F. It would also be desirable to maximize thermal performance of a cold plate while mitigating change in pressure drop through the cold plate. It would be desirable with regard to heat exchangers to either reduce the number of cold plates needed to achieve a certain effectiveness, or to achieve a higher effectiveness for a given number of cold plates.
The foregoing examples and limitations associated therewith are intended to be illustrative and not exclusive. Other limitations of the related art will become apparent to those of skill in the art upon reading of the specifications and study of the drawings.